At four-thirty one Saturday afternoon the laws of physics as we know them underwent a change. Electronic devices, cars, industries stopped. The lights went out. Any technology more complicated than a lever or pulley simply wouldn't work. A new set of rules took its place—laws that could only be called magic. Ninety-nine percent of humanity has simply vanished. Cities lie abandoned. Supernatural creatures wander the silenced achievements of a halted civilization.

Pete Garey has survived the Change and its ensuing chaos. He wanders the southeastern United States, scavenging, lying low. Learning. One day he makes an unexpected friend: a smartassed unicorn with serious attitude. Pete names her Ariel and teaches her how to talk, how to read, and how to survive in a world in which a unicorn horn has become a highly prized commodity.

When they learn that there is a price quite literally on Ariel's head, the two unlikely companions set out from Atlanta to Manhattan to confront the sorcerer who wants her horn. And so begins a haunting, epic, and surprisingly funny journey through the remnants of a halted civilization in a desolated world.